Triple-diametric rectifier-connections



Feb. 25, 1958 J. L. BOYER ETAL TRIPLE-DIAMETRIC RECTIFIER-CONNECTIONSFiled March 19, 1954 All United States Patent 2,825,022 TRIPLE-DIAMETRICRECTIFIER-CONNECTIONS John L. Boyer, Pittsburgh, Pa., and Charles R.Marcuru, Newton Highlands, Mass., assignors to Westinghouse ElectricCorporation, East Pittsburgh, Pa., 21 corporation of PennsylvaniaApplication March 19, 1954, Serial No. 417,334

21 Claims. (Cl. 321-26) Our invention relates to improvements intriple-diametric rectifier-connections, or other electric-power translation-systems, whereby over-all economies are obtained, and betteroperation.

A triple-diametric rectifier-connection, with a six-anode mercury-arcrectifier, has been known, at least as early as 1930, as shown by theMarti-Winograd book on Mercury-Arc Rectifiers, first ed., 1930, chapter6, page 180, Table V.-E. A triple-diametric connection for a sixanodemercury-arc rectifier, with the addition of a special load-balancingreactor or interphase transformer having an air-gapped core having asmaller-sectioned magnetizable core-part bypassing the air gap, wasshown in the Maslin Patent 1,979,669, granted November 6, 1934. Anapplication of the triple-diametric connection to igni: trons orsingle-anode rectifiers, but without the air-gapped core with abypassing small-sectioned magnetizable part, was shown in a twenty-pagetrade-publication entitled Oerlikon Mercury-Arc Rectifiers, Circular1618.E, dated March 1951, Fig. 23c, page 15, published by Ateliers deConstruction Oerlikon, Zurich 50, Switzerland.

According to our present invention, we are providing several differentconnection-assemblies having certain advantages, for certain purposes,in connection with the broad field of triple-diametric connections forrectifiers or asymmetrically conducting devices in general; and alsoincluding improvements which are directed to the application of theprinciple of the air-gapped core with a reduced-section bypassingmagnetizable part, to the broad field of triple-diametric connectionsfor a plurality of entirely separate single-phase asymmetricallyconducting devices of a type in which the rating of each device isdetermined more by the peak current carried by the device, than by theaverage current or by the thermal capacity of the device.

This last-mentioned phase of our invention is predicated upon thefollowing facts. A triple-diametric rectifier-connection requires alarger transformer than a double-Y connection. In large ignitrons, orsingleanode vaporizable-cathode rectifiers, with a large diameter oftank, and with large spacings within the tank, the rating of each tankis determined by the peak current, rather than the average current. Theare within such a tube or tank is extinguished at the end of eachcurrent-conducting period, and the amount of ionization, and hence itsrate of decay at the end of each conducting-period, is dependent uponthe peak loadcurrent so that the arc-back rate is determined by the peakcurrent and not by the average current. In a multianode rectifier, onthe other hand, an arc is playing at all times within the tank, said areterminating on a cathode-pool which is common to all of the anodes, sothat the peak anode current does not have the same importance.

Present designs of large ignitron tubes also have an anode which has ananode-surface area which is more than enough for the radiation of theheat-losses on the anode, to the walls of the tube, so that the currentfl ce rating of the tube is not limited by its thermal capacity; in otherwords, there is an excess of thermal capacity. As compared to thedouble-Y connection of ignitrons, our triple-diametric connection takesfull advantage of this reserve thermal capacity which is inherent in theigintron, as well as the 3-to-2 reduction in the peak current carried byeach tube, as compared with a double Y connection.

Added to all this, it may be noted that the lower peak current and thelonger conduction-period of the triple-diametric connection of ignitronsresults in a lower arc-drop, meaning a higher efiiciency of therectifier; there is an 18% reduction in the current in eachrectifier-phase, thus reducing the current-rating requirements of theanode-breakers and the transformer-bushings; and there is a 42%reduction, or other considerable reduction, in the magnitude of thefault-currents or crest arc-back currents, thus reducing the requiredamount of transformer-bracing, reducing the current-interruptionrequirements of the anode-breakers, and reducing the chance of damagingthe rectifiers themselves. When all of these facts are taken intoconsideration in the design of the complete equipment, there is anover-all gain of the order of 15 or 20% in rating, in changing from thedouble-Y to the triple-diametric connection of ignitrons.

Since the triple-diametric connection involves a serious voltage-rise atlow loads, which seriously limits the utility of this connection, it isusually necessary to provide the bypassed air gap of the Maslin patent,before the fullest advantage can be taken of our invention, the effectof this bypassed air gap being to reduce the minimum useful load, whichdoes not involve a voltagerise, to a value which is small enough to beeconomically taken care of by a small permanently connected dummyload,which does not detract too seriously from the efficiencies and economieswhich are obtained by our invention.

In the application of our triple-diametric connections tosemiconductor-rectifiers, it is to be noted that, in this kind ofrectifier, the voltage-drop is determined by the peak-current, so thatthe reduction in this peakcurrent not only increases the ratings of thesemiconductor-rectifiers but reduces the losses, thus increasing theefliciency. Semiconductor-rectifiers are also particularly susceptibleto damage depending upon the magnitude of the fault-currents to whichthey are subjected, and hence the 42% reduction in the magnitude of thefault-current is of particular significance in the application of ourinvention to semiconductor-rectifiers.

As a result of the foregoing and other considerations, it will be seenthat we obtain significant rating-increases, cost-reductions, betterefiiciencies, and less damage from fault-currents, in our completeassembly of rectifiers, transformers and breakers, by using theprinciples of our present invention.

With the foregoing and other objects in view, our invention consists inthe circuits, systems, apparatus, combinations, parts and methods ofdesign and operation, hereinafter described, and illustrated in theaccompanying drawing, in which:

Fig. l is a schematic circuit diagram illustrating one embodiment of theinvention; and

Figs. 2, 3 and 4 are similar diagrams illustrating modified embodimentsof the invention.

Fig. 1 shows a basic form of the invention, using six ignitrons orentirely separate single-phase rectifiers R1 to R6, or otherasymmetrically conducting devices of a type in which the rating of eachdevice is determined more by the peak current carried by the device thanby the thermal capacity of the device. Each rectifier may comprise asingle main anode 7, a grid 8, an ignitor or makealive electrode 9, anda cathode-pool 10, usually of mercury or other vaporizable metal. Thus,each of the six rectifiers R1 to R6, in Fig. l, constitutes avapor-electric device having a single-phase space-current path betweenan anode-means and a cathode-means, and each vaporelectric device hasits "own individual cathode-means.

Our invention relates to electric-power translationsystems of "the typein which triple-diametric connections of a plurality of entirelyseparate single-phase asymmetrically conducting devices are used tointerchange power, in one direction or the other, between a firstpolyphase system and a second system which may be cit er a direct-,current system or an alternating-current system having a frequencywhich is different from said first polyphase sys- 'tem.

The rawing shows electric-power translation-systems of the type in whichpower is taken from a three-phase power-supply system, including thepower-leads A, B and C, and is transmitted, through anasymmetric-conductor assembly, to a unidirectional-current load-circuit,having the power-leads (l) and In order to greatly simplify the languagewhich is necessary to'explain the invention, it will be described as ifthe power is transferred from the three-phase power-leads A, B and C tothe unidirectional-current power-leads and but it is to be distinctlyunderstood that, by the use of simple and well-known invertercontrol-connections, the direction of power-flow could be reversed. Forthe same purpose of greatly simplifying the language necessary toexplain the invention, the unidirectional-current power-leads and willbe described as if they were a direct-current power-line which receivespower from the three-phase power-line A, B, C, but it is to bedistinctly understood that the unidirectionalcurrent line could beeither the anode-terminal circuit or the cathode-terminal circuit of onephase (or the phase) of a second, diiierent-frequency,alternatingcurrent system which receives power from, or which transmitspower to, the three-phase system A, B, C, provided that suitablerectifier-controlling means are provided, as shown, for example, in theBoyer and Hagensick application Serial No. 307,294, filed August 30,1952, now Patent No. 2,707,258 of April 26, 1955, or any modification orvariation thereof.

In Fig. 1, there are three 2-phase power-leads A, B, C, supplying powerto a power-transformer, which may be either a 3-phase transformer or anassembly of suitably connected single-phase transformers, as will bereadily understood. The power-transformer is provided with a 6-phasesecondary winding, having terminals numbered from 1 to 6, according tothe phase sequence. In Fig. 1,

the three single-phase secondary windings which are pro- 7 vided withthe pairs of diametrically opposite terminals, such as 14, 36, and 5-2,are provided with separate or unconnected midtaps A, B and C,respectively.

In Fig. 1, the direct-current power-leads are indicated at andrespectively. R6 are connected, in individual rectifier-phases orcircuits, between the positive direct-current lead and the six secondaryterminals 1 to 6 which constitute 6-phase power-leads for theserectifiers. Usually, each rectifierphase also includes an anode-breaker15. The three separate secondary midtaps A, B and C are connected, inthree separate circuits, to the negative direct-current lead Theconnections thus described are the triple-diametric connections, whichpractically amount to three doublewave single-phase rectifiers which areenergized in ac cordance with the three phases A, B and C. It is usuallydesirable, in such triple-diametric connections, to provide aload-balancing reactor-means, for substantially balancing the directcurrents of the respective rectifiers. This need arises from the factthat the triple'diametric rectifier-connections are such that differentrectifier-phases 1 to 6, which are energized by the instantaneousvoltages of different phases of the polyphase circuit, are at timesoperated so as to be conducting in parallel with each other,

The six rectifiers R1 to so as to simultaneously supply power to, orreceive power from, the same unidirectional-current power-circuit orbus. Heretofore, a suitable load-balancing reactor-means, or interphasereactance-rneans, as it might be called, has been serially included, insome way, in these rectifiereonnections, so that this interphasereactance-means will develop the instantaneous voltage-difierences whichare necessary to permit the parallel operation of a plurality ofrectifier-phases having terminal-voltages which do not reach their peaksat the same instant. Such an interphase reactance-means is capable ofabsorbing or developing the necessary alternating-currentvoltage-diiferences or ripples, to permit such parallel operation ofrectifier-phases, and in this ripple-balancing sense it may be regardedas a means for balancing the unidirectional currents of theparallel-operating rectifier-phases.

in Fig. 1, we have provided a novel form of such load-balancing means,in the form of three separate reactor-means A, B" and C, each having itsown individual air-gapped magnetizable core 29, for balancing thetotal'direct currents of said three double-wave singlephase connections,in pairs. Thus, the core 2% of the reactor A is provided with twowindings 21 and 22, the core 20 of the reactor B is provided with twowindings 23 and 24, and the core 29 of the reactor C is provided withtwo windings 25 and 26. The windings 21 and 24 are serially connectedbetween the midtap A and the negative lead while the windings 23 and 26are similarly connected between the midtap B and said negative lead andthe windings 25 and 22 are connected between the midtap C and thenegative lead The direct-current components which are carried by thethree midtaps A, B and C are thus balanced, in pairs, since thereactor-windings 21 to 26 all have the same number of turns, and thereactors are otherwise similar to each other.

In accordance with the principles described in the Maslin patent, eachof the reactor-cores 2% has a cross-section which is large enough forthe expected unbalanced currents, each has an air gap 27 therein for thepurpose of preventing core-saturation during the flow of heavyunbalanced currents, and each has a smalLsectioned magnetizablecore-part 2% which bypasses the air gap 2? to reduce the magnetizingcurrent of the reactor at very low direct-current loads on therectifier-assembly. Our three 2-coil load-balancing reactors A, B and Cthus act more individually than a 3-phase reactor, and the threeindividual reactor-cores 2i are susceptible to more individualdesign-treatment than would be the case with a 3-phase core. If there isan unbalance in current in the two windings which are placed on any oneof the cores 20, a flux will be produced, in that core, which induces avoltage in the windings, which tends to balance the two currents, oneagainst the other. I

' In Fig. 1, we have shown a small-current permanently connectedresistance-load 29, which is connected across the direct-currentpower-leads and for the purpose of adapting the device for use withdirect-current systems in which the load-current may fall to zero or toa value below the critical value at which the lay-passing core-sections223 permit a voltage-rise. It will be understood that this smalldummy-load 29 could be used in any of the other forms of embodiment ofour invention. In the case of inverter-operation, the dummyresistanceload 29 would be placed across the alternating-current leads,which would then constitute the load-leads or output-leads of theassembly.

Fig. 2 shows a modified form of our circuit, in which thereactor-windings 21 to 26 are placed in the anodeeads or in therespective rectifier-phases. In this case, the two'windings of each pairof diametrically opposite phases are put on an individual magnetizablecore-leg 20', and each of these individual legs is preferably providedwith its own air gap 27 and reducedsection bypassing core-part 28, aspreviously described. in 2, as further indicating a possible change indesign, the

three core-legs 20 are legs or phases of a 3-phase reactorcore 30, eachcore-phase or leg 20 carrying two diametrically opposite windings. inFig. 2, since the load-balancing reactors are in the anode-leads orrectifier-phases, the secondary winding of the power-transformer may beconnected as a star-connected 6-phase secondary, having a commonstar-point connection N, which is connected to the negativedirect-current lead The operation of the apparatus shown in Fig. 2 issimilar to that which is shown in Fig. 1, with the changes noted, exceptthat the anode-lead connections, in Fig. 2, may serve to limit thearc-back current, or fault current, in any rectifier, somewhat betterthan is the case with the reactor-connections of Fig. 1, for example.

Pig. 3 shows a still further form of application of our triple-diametricconnections, in which the currents in the three phases can be differentfrom each other. In this case, instead of using the load-balancingmutual reactances A, B" and C of Figure 1, we use self-inductancedevices or reactors A", B' and C, each having an air-gapped magnetizablecore 31, and each having an individual winding 32 which is connectedbetween the negative lead and the appropriate midtap A, B or C, as thecase may be. The circuit of Fig. 3 can be used in applications where itis desirable to be able to remove some of the tubes R1 to R6 fromoperation, without substantially changing the average direct-currentvoltage.

In the three forms of embodiment which we have thus far shown, for ourinvention, We have shown a 3-phase system of double-wave single-phaserectifiers in which a midtap of the transformer-winding is used for thereturncircuit of the rectifiers. We wish it to be understood, however,that in general, a bridge-type rectifier-connection can be used, inwhich twice as many individual rectifiers will have to be used, and inwhich each of the six rectifierphases or circuits contains, in effect,two rectifiers in series with each other, so that the voltages of thepowerleads can be doubled, throughout.

We have shown such a rectifier-bridge circuit in Fig. 4, in which thethree secondary phases 1-4, 3-6 and 52 are the same as in Fig. l or inFig. 3, without the midtaps A, B or C. In additionto the six previouslydescribed rectifier-units R1 to R6, our Fig. 4 connection uses six moreunits, with primed numbers, R1 to R6, each connected in a direct-currentcircuit or branch in series with its correspondingly numberedrectifier-unit without the prime, so as to provide threerectifier-bridges, (-)-R11-R1BAR44R4'; ()-R33- R3-BBR6-6R6; and(-)R55R5BC-- R2-2--R2'.

The three bridge-points BA, BB and BC in Fig. 4 are connected to thepositive direct-current lead through any suitable load-balancingreactor-means, such as a threephase reactor-core 50 whichis providedwith reactorwindings XA, X8 and XC which are disposed on the severallegs or phases of the three-phase core 50; or any other suitableload-balancing means could be used, such as the means shown in Fig. 1.Preferably, the individual reactor-legs of the three-phase reactor-core59 in Fig. 4 are each provided with an air gap 27, which is bypassed bya reduced-section core-part 28, as previously described. Therectifier-bridge connection of Fig. 4 has the advantage that 180conduction is maintained in the rectifying devices, thus producing aminimum loss, and making the possible maximum fault-current considerablylower in value. The inductance of each leg of the reactor 50 preventsheavy fault-currents from being sent back from the direct-current leadsand to any faulted rectifier-unit.

In Fig. 1, We have shown the rectifiers as being ignitrons. In Figs. 2,3 and 4, we have shown the rectifiers by means of a conventionalrectifier-symbol, which is intended to be applicable to any kind ofrectifier. In carrying out our invention, in any of its forms ofembodiment, we contemplate that, in each case, each in- 6 dividualrectifier shall be of a type in which the rating is determined by thepeak-current rather than by the thermal capacity of the rectifier. Twooutstanding forms of such rectifiers were discussed in the openingportions of our description, namely the ignitron and any one of thelarge number of forms of static or semiconductor rectifiers, and wedesire that our invention shall be understood as including the use ofeither one of these two general types of rectifiers.

While we have illustrated our invention in only four suggestedillustrative forms, we wish it to be understood that our invention isnot limited to these particular forms, and that it is susceptible ofvarious modifications and substitutions of equivalents, withoutdeparting from the essential spirit of the invention.

We claim as our invention:

1. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apower-transformer connected be tween said three-phase power-leads andsaid six-phase power-leads, a plurality of entirely separatesingle-phase asymmetrically conducting devices of a type in which therating of each device is determined more by the peak current carried bythe device than by the average current of the device, and atriple-diametric connectionmeans for providing three double-wavesingle-phase connections for operatively connecting said asymmetricallyconducting devices between said direct-current powerleads and the threepairs of diametrically opposite terminals of said six-phase power-leads,said triple-diametric connection-means including a load-balancingreactormeans for substantially balancing the direct currents of therespective asymmetrically conducting devices, and said load-balancingreactor-means having one or more airgapped magnetizable cores having acore-section large enough for the expected unbalanced currents, andhaving a smaller-sectioned magnetizable core-part bypassing the air gapto reduce the magnetizing currents of the loadbalancing reactor-means atvery low loads.

2. The invention as defined in claim 1, characterized by each of theasymmetrically conducting devices being a vapor-electric device having asingle-phase space-current path between an anode-means and acathode-means, each vapor-electric device having its own individualcathode-means.

3. The invention as defined in claim 1, characterized by each of theasymmetrically conducting devices being a semiconductor-rectifier.

4. The invention as defined in claim 1, in combination with a means forpermanently connecting a small-current load-means across the outputpower-leads of said triplediametric connection-means, thecurrent-consumption of said small-current load-means correspondingapproximately to the aforesaid very low loads.

5. The invention as defined in claim 1, characterized by each of thethree double-wave single-phase connections including four asymmetricallyconducting devices in a bridge-connection.

6. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apowertransformer connected between said three-phase power-leads and saidsix-phase power-leads, a plurality of entirely separate single-phaseasymmetrically conducting devices of a type in which the rating of eachdevice is determined more by the peak current carried by the device thanby the average current of the device, and a triple-diametricconnection-means for providing three double-wave single-phaseconnections for operatively connecting said asymmetrically conductingdevices between said direct-current power-leads and the three pairs ofdiametrically opposite terminals of said six-phase power-leads, saidtriple-diametric connectionmeans including three separate load-balancingreactormeans, each having its own individual air-gapped magnetizablecore, for substantially balancing the total direct currents of saidthree double-wave single-phase connections, in pairs.

7. The invention as defined in claim 6, characterized by each air-gappedreactor-core having a core-section large enough for the expectedunbalanced currents, and having a smaller-sectioned magnetizablecore-part bypassing the air gap to reduce the magnetizing currents ofthe load-balancing reactor-means at very low loads.

8. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apower-transformer connected between said three-phase power-leads andsaid six-phase power-leads, a plurality of entirely separatesingle-phase asymmetrically conducting devices of a type in which therating of each device is determined more by the peak current carried bythe device than by the average current of the device, and atriple-diametric connection-means for providing three double-Wavesingle-phase connections for operatively connecting said asymmetricallyconducting devices between said direct-current power-leads and the threepairs of diametrically opposite terminals of said sixphase power-leads,said triple-diametric connectionmeans including a three-phaseload-balancing reactor having a three-phase magnetizable core, eachphase of said reactor-core having winding-means thereon for excitingsaid phase in accordance with the total direct current in a differentone of said three double-wave single-phase connections, forsubstantially balancing said total direct currents, each phase of saidreactor-core further having an air gap therein, and having acore-section large enough for the expected unbalanced currents, andhaving a smallersectioned magnetizable core-part by-passing the air gapto reduce the magnetizing currents of the load-balancing reactor at verylow loads.

9. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apower-transformer connected between said three-phase power-leads andsaid six-phase power-leads, said power-transformer providing a separatemidtap lead for each of the three pairs of diametrically oppositeterminals of the six-phase power-leads, a plurality of entirely separatesingle-phase asymmetrically conducting devices of a type in which therating of each device is determined more by the peak current carried bythe device than by the average current of the device, three separatereactor-means, each having its own individual airgapped magnetizablecore, a means for connecting said asymmetrically conducting devicesbetween one of said direct-current power-leads and said six-phasepower-leads, respectively, and a means for connecting said threeseparate reactor-means between another of said direct-currentpower-leads and said three separate midtap leads, respectively.

10. The invention as defined in claim 9, characterized by each of saidthree separate reactor-means being a twowinding load-balancingreactor-means, having its two windings in series-circuit connection totwo diflerent midtap means, respectively, for substantially balancingthe direct currents of the respective midtap means, in pairs.

11. The invention as defined in claim 10, characterized by eachair-gapped reactor-core having a core-section large enough for theexpected unbalanced currents, and having a smaller-sectionedmagnetizable core-part bypassing the air gap to reduce the magnetizingcurrents of the loadbalancing reactor-means at very low loads.

12. The invention as defined in claim 9, characterized by each of saidthree separate reactor-means being a singlephase reactor.

13. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apower-transformer connected between said three-phase power-leads andsaid six-phase power-leads, a plurality of entirely separatesingle-phase asymmetrically conducting devices of a type in which therating of each device is determined more by the peak current carried bythe device than by the average current of the device, a means forconnecting said asymmetrically conducting devices in six separatephase-connections between one of said direct-current power-leads andsaid sixphase power-leads, respectively, said six separatephaseconnections including a load-balancing reactor-means forsubstantially balancing the tota'lized direct-currents in the threepairs of diametrically opposite phase-connections, and a means forproviding an opposite-potential connection between another of saiddirect-current power-leads and the power-circuits for said six separatephase-connections.

14. The invention as defined in claim 13, characterized by saidload-balancing reactor-means having one or more air-gapped magnetizablecores having a core-section large enough for the expected unbalancedcurrents, and having a smaller-sectioned magnetizable core-partbypassing the air gap to reduce the magnetizing currents of theloadbalancing reactor-means at very low loads.

15. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power-leads, apower-transformer having a threephase winding-connection which isconnected to said threephase power-leads, and a star-connected six-phasewindingconnection which is connected to said six-phase powerleads, aplurality of entirely separate single-phase asymmetrically conductingdevices of a type in which the rating of each device is determined moreby the peak current carried by the device than by the average current ofthe device, a means for connecting said asymmetrically conductingdevices in six separate phase-connections between one of saiddirect-current power-leads and said six-phase power-leads, respectively,said six separate phase-connections including a load-balancingreactor-means for substantially balancing the totalized direct-currentsin the three pairs of diametrically opposite phase-connections, and ameans for providing an opposite-potential connection between another ofsaid direct-current power-leads and the star point of saidstar-connected six-phase windingconnection.

16. The invention as defined in claim 15, characterized by saidload-balancing reactor-means having one or more air-gapped magnetizablecores having a core-section large enough for the expected unbalancedcurrents, and having a smaller-sectioned magnetizable core-partbypassing the air gap to reduce the magnetizing currents of theload-balancing reactor-means at very low loads.

17. An electric-power translation-system, including direct-currentpower-leads, three-phase power-leads, sixphase power leads, apower-transformer having a threephase winding-connection which isconnected to said three-phase power-leads, and a star-connectedsix-phase winding-connection which is connected to said six-phasepower-leads, a plurality of entirely separate single-phaseasymmetrically conducting devices of a type in which the rating of eachdevice is determined more by the peak current carried by the device thanby the average current of the device, and a means for connecting saidasymmetrically conducting devices in six separate phaseconnectionsbetween one of said direct-current powerleads and said six-phasepower-leads, respectively, said six separate phase-connections includinga three-phase load-balancing reactor having a three-phase magnetizablecore, each phase of said reactor-core having two windings thereon, forexciting said phase with the sum of the direct currents flowing in thetwo phase-connections of a different pair of diametrically oppositephase-connections.

18. The invention as defined in claim 17, characterized by each phase ofthe reactor-core further having an air gap therein, and having acore-section large enough for the expected unbalanced currents, andhaving a smaller-sectioned magnetizable core-part bypassing the air gapto reduce the magnetizing currents of the loadbalancing reactor at verylight loads.

19. An electric-power translation-system, including direct-currentpower-leads, three-phase powerleads, sixphase power-leads, apower-transformer connected between said three-phase power-leads andsaid six-phase power-leads, a plurality of entirely separatesingle-phase asymmetrically conducting devices of a type in which therating of each device is determined more by the peak current carried bythe device than by the average current of the device, and atriple-diametric connection-means for providing three double-wavesingle-phase connections for operatively connecting said asymmetricallyconducting devices between said direct-current power-leads and the threepairs of diametrically opposite terminals of said six-phase power-leads,each of the three double-wave single-phase connections including fourasymmetrically conducting devices in a bridge-connection, saidtriplediametric connection-means including a load-balancingreactor-means for substantially balancing the currents in the threedouble-wave single-phase connections.

20. An electric-power translation-system, including:unidirectional-current power-leads; three-phase powerleads; six-phasepower-leads; a power-transformer-means, connected between saidthree-phase power-leads and said six-phase power-leads; anasymmetric-conductor assembly having six phase-circuits, saidasymmetric-conductor assembly comprising a plurality of entirelyseparate singlephase asymmetrically conducting devices of a type inwhich the rating of each device is determined more by its peak currentthan by its average current; a triplediametric connection-means forproviding three doublewave single-phase connections for operativelyconnecting said asymmetrically conducting devices between saidunidirectional-current power-leads and the three pairs of diametricallyopposite terminals of said six-phase powerleads; and an interphasereactance-means which is serially included in said connection-means,said interphase reactance-means comprising a plurality of air-gappedmagnetic core-members having a core-section large enough for theexpected unbalanced currents, and having a smaller-sectionedmagnetizable core-part bypassing the air gap to reduce the magnetizingcurrents of the load- 1O balancing reactor-means at very low loads, eachcoremember having thereon windings for developing the instantaneousvoltage-differences which are necessary to permit a plurality ofasymmetric-conductor phases to operate in parallel wtih each other attimes.

21. An electric-power translation-system.including:unidirectional-current power-leads; three-phase powerleads; six-phasepower-leads; a power-transformer-means, connected between saidthree-phase power-leads and said six-phase power-leads; a vapor-electricassembly having six phase-circuits, said vapor-electric assemblycomprising a plurality of vapor-electric devices, each having asingle-phase space-current path between an anode-means and acathode-means, each vapor-electric device having its own individualcathode-means; a triple-diametric connection-means for providing threedouble-wave singlephase connections for operatively connecting saidvaporelectric devices between said unidirectional-current powerleads andthe three pairs of diametrically opposite terminals of said six-phasepower-leads; and an interphase reactance-means which is seriallyincluded in said connection-means, said interphase reactance-meanscomprising a plurality of air-gapped magnetic core-members having acore-section large enough for the expected unbalanced currents, andhaving a smaller-sectioned magnetizable core-part bypassing the air gapto reduce the magnetizing currents of the load-balancing reactor-meansat very low loads, each core-member having thereon windings fordeveloping the instantaneous voltage-differences which are necessary topermit a plurality of vaporelectric phases to operate in parallel witheach other at times.

References Cited in the file of this patent UNITED STATES PATENTS1,211,380 Thomas Ian. 2, 1917 1,976,580 Rose Oct. 9, 1934 1,979,699Maslin Nov. 6, 1934 2,069,283 Slepian et al. Feb. 2, 1937

